Cooling system and method for cooling radio unit

ABSTRACT

At least one heat generating radio unit in an active antenna system unit, the cooling system comprising at least one fan and an air duct, where each heat generating radio unit to be cooled by the cooling system is arranged connected to a heat sink unit comprising cooling fins, the heat sink unit being arranged to transfer heat between the radio unit and the ambient air, where the at least one fan is arranged to generate a primary air flow of ambient air in the air duct between at least one air duct inlet and at least one air duct outlet, where the air duct is arranged to extend in the longitudinal direction (A) of the active antenna system unit along each of the said heat sink units and to border on each of the said heat sink units.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No. PCT/EP2012/058812, filed on May 11, 2012, which is hereby incorporated by reference in its entirety.

FIELD OF THE APPLICATION

The present application relates to a cooling system for cooling at least one heat generating radio unit in an active antenna system unit. The application also relates to a method for cooling at least one heat generating radio unit in an active antenna system unit.

BACKGROUND OF THE APPLICATION

As the efficiency of e.g. power amplifiers and other components in radio units is not 100%, radio units emit heat, i.e. the radio unit comprises heat generating components whereby the radio unit needs to be cooled. The radio unit may be cooled using a heat sink by thermally connecting the radio unit against the heat sink base in order to be able to transfer heat from the radio unit to the heat sink and from there to the ambient air. The heat sink is further generally arranged with cooling fins in order to improve the cooling of the radio unit.

If more cooling power is needed, it is possible to arrange forced cooling of the heat sink, i.e. to arrange a fan that forces a flow of air across the surfaces of the cooling fins of the heat sink thereby replacing air heated by the heat from the cooling fins with cooler ambient air from the outside of the heat sink, thus improving the cooling of the heat sink.

In order to reduce Radio Frequency loss and to save energy without affecting radio performance, a telecom radio unit, e.g. a radio transceiver, is preferably arranged as close as possible to the antenna. This also enables reduction of radio unit volume, weight and cost. Thus, a radio unit is preferably installed or mounted directly on the antenna (i.e. semi-integrated installation) or integrated with the antenna (i.e. integrated installation) on top of a tower or at a similar high mounting position in an active antenna system unit. The active antenna system unit is generally arranged with one end of its longitudinal extension more or less below the other, i.e. arranged more or less in a vertical position, depending on the preferred positioning of the antenna or antennas of the active antenna system unit. The heat sinks of the radio units are arranged with cooling fins extending along the longitudinal extension of the active antenna system unit in order to improve the natural cooling. If more than one radio unit is arranged together with an antenna in an active antenna system unit, the radio units are arranged displaced along the longitudinal extension of the active antenna system unit, i.e. along the longitudinal extension of the antenna or antennas in order to protrude as little as possible outside the antenna face, thereby minimizing the transversal dimensions of the active antenna system unit.

Due to the often limited base area of a heat generating component in a radio unit and the desire to place more and more functionality on a defined base area of a component, more and more powerful components are developed, e.g. higher integration components. This increase in component capacity leads to that more power can be fed to components per component base area than before which in turn results in that the components emit more heat per base area than before when in maximum use e.g. during peak load in telecom systems, i.e. the maximum heat load of components is increasing as they may be fed with more power per square centimetre (W/cm2) base area. This is also the case for components for radio units.

As mentioned above, increased cooling power for a radio unit heat sink is traditionally achieved by increasing the cooling fin area, e.g. by arranging higher cooling fins, or by arranging a forced cooling. The drawback with these solutions is that the cooling fin dimensions can not be increased indefinitely due to manufacturing difficulties and cost, and that the mounting of cooling fans affect the natural cooling when the fans are not in operation.

SUMMARY OF THE APPLICATION

The object of the present application is to provide an improved cooling system for cooling at least one heat generating radio unit in an active antenna system unit and an improved method for cooling at least one heat generating radio unit in an active antenna system unit.

The object is achieved by arranging a cooling system for cooling at least one heat generating radio unit in an active antenna system unit, the cooling system comprising at least one fan and an air duct, where each heat generating radio unit to be cooled by the cooling system is arranged connected to a heat sink unit comprising cooling fins, the heat sink unit being arranged to transfer heat between the radio unit and the ambient air, where the at least one fan is arranged to generate a primary air flow of ambient air in the air duct between at least one air duct inlet and at least one air duct outlet, where the air duct is arranged to extend in the longitudinal direction of the active antenna system unit along each of the said heat sink units and to border on each of the said heat sink units, where the primary air flow generated in the air duct is arranged to flow substantially in the longitudinal direction of the active antenna system unit and is further arranged to generate a secondary air flow of ambient air over a number of cooling fins of each of the said heat sink units, and where the cooling fins to be cooled by the secondary air flow are arranged oriented at an angle with respect to the longitudinal direction of the active antenna system unit.

The object is further achieved by a method for cooling at least one heat generating radio unit in an active antenna system unit using a cooling system, the cooling system comprising at least one fan and an air duct, the method comprising the steps of: connecting each heat generating radio unit to be cooled by the cooling system to a heat sink unit comprising cooling fins, arranging the heat sink unit to transfer heat between the radio unit and the ambient air, arranging the at least one fan to generate a primary air flow of ambient air in the air duct between at least one air duct inlet and at least one air duct outlet, arranging the air duct to extend in the longitudinal direction of the active antenna system unit along each of the said heat sink units and to border on each of the said heat sink units, arranging the primary air flow generated in the air duct to flow substantially in the longitudinal direction of the active antenna system unit and further arranging the primary air flow to generate a secondary air flow of ambient air over a number of cooling fins of each of the said heat sink units, and arranging the cooling fins to be cooled by the secondary air flow to be oriented at an angle with respect to the longitudinal direction of the active antenna system unit.

By arranging a cooling system for cooling at least one heat generating radio unit in an active antenna system unit, where each heat generating radio unit to be cooled by the cooling system is arranged connected to a heat sink unit comprising cooling fins and where at least one fan is arranged to generate a primary air flow of ambient air in an air duct between at least one air duct inlet and at least one air duct outlet, where the air duct is arranged to extend in the longitudinal direction of the active antenna system unit along each of the said heat sink units and to border on each of the said heat sink units, where the primary air flow generated in the air duct is arranged to flow substantially in the longitudinal direction of the active antenna system unit and is further arranged to generate a secondary air flow of ambient air over a number of cooling fins of each of the said heat sink units, and where the cooling fins to be cooled by the secondary air flow are arranged oriented at an angle with respect to the longitudinal direction of the active antenna system unit, the longitudinal extension of the cooling fins to be cooled by the ambient air flow can be reduced whereby the temperature of the ambient air flow at the downstream end of the respective cooling fin can be reduced, thus increasing the cooling power at this position of the respective heat sink which is especially advantageous when using radio units with heat sinks having large dimensions in the longitudinal direction of the active antenna system unit. A further advantage is that the air duct and the fan does not affect the natural cooling when the at least one fan is shut off in situations where forced cooling is not needed, e.g. when the ambient temperature is so low that natural cooling is enough. A further advantage is that the at least one fan and air duct do not increase the volume of the active antenna system unit significantly.

By arranging a method for cooling at least one heat generating radio unit in an active antenna system unit using a cooling system comprising the steps of: connecting each heat generating radio unit to be cooled by the cooling system to a heat sink unit comprising cooling fins, arranging the heat sink unit to transfer heat between the radio unit and the ambient air, arranging at least one fan to generate a primary air flow of ambient air in an air duct between at least one air duct inlet and at least one air duct outlet, arranging the air duct to extend in the longitudinal direction of the active antenna system unit along each of the said heat sink units and to border on each of the said heat sink units, arranging the primary air flow generated in the air duct to flow substantially in the longitudinal direction of the active antenna system unit and further arranging the primary air flow to generate a secondary air flow of ambient air over a number of cooling fins of each of the said heat sink units, and arranging the cooling fins to be cooled by the secondary air flow to be oriented at an angle with respect to the longitudinal direction of the active antenna system unit, the longitudinal extension of the cooling fins to be cooled by the ambient air flow can be reduced whereby the temperature of the ambient air flow at the downstream end of the respective cooling fin can be reduced, thus increasing the cooling power at this position of the respective heat sink which is especially advantageous when using radio units with heat sinks having large dimensions in the longitudinal direction of the active antenna system unit. A further advantage is that the air duct and the fan does not affect the natural cooling when the at least one fan is shut off in situations where forced cooling is not needed, e.g. when the ambient temperature is so low that natural cooling is enough. A further advantage is that the at least one fan and air duct do not increase the volume of the active antenna system unit significantly.

According to one embodiment of the application, the at least one air duct outlet is arranged to direct a flow of ambient air over a number of cooling fins of each of the heat sink units.

According to one embodiment of the application, the at least one air duct outlet is arranged along a longitudinal side of the active antenna system unit.

According to one embodiment of the application, the gap size of the air duct outlet is arranged with varying dimensions along the longitudinal direction of the active antenna system unit.

According to one embodiment of the application, a cover is arranged at the air duct to direct the air flow leaving the air duct outlet towards the surface of the heat sink unit.

According to one embodiment of the application, the at least one air duct inlet is arranged to suck a secondary air flow of ambient air over a number of cooling fins of each of the said heat sink units.

According to one embodiment of the application, the at least one air duct inlet is arranged along a longitudinal side of the active antenna system unit.

According to one embodiment of the application, the gap size of the air duct inlet is arranged with varying dimensions along the longitudinal direction of the active antenna system unit.

According to one embodiment of the application, the angle between a cooling fin and the longitudinal direction of the active antenna system unit is arranged to vary along the extension of the cooling fin.

According to one embodiment of the application, a cooling fin is arranged with varying dimensions along the longitudinal extension of the cooling fin.

According to one embodiment of the application, a cooling fin is arranged wave formed or with curved shape along the longitudinal extension of the cooling fin.

According to one embodiment of the application, the at least one fan is a centrifugal fan.

According to one embodiment of the application, the method for cooling a heat generating unit can comprise the step of arranging the at least one air duct outlet to direct a flow of ambient air over a number of cooling fins of each of the heat sink units.

According to one embodiment of the application, the method for cooling a heat generating unit can comprise the step of arranging the at least one air duct inlet to suck a secondary air flow of ambient air over a number of cooling fins of each of the heat sink units.

Further advantages of the application will be apparent from the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The appended drawings are intended to clarify and explain different embodiments of the present application in which:

FIG. 1 shows a schematic view of a cooling system according to a first embodiment of the application for cooling at least one heat generating radio unit in an active antenna system unit,

FIG. 2 shows another schematic view of the cooling system according to FIG. 1,

FIG. 3 shows a schematic cross-section of an air duct according to one embodiment of the application,

FIG. 4 shows another schematic cross-section of an air duct according to one embodiment of the application,

FIG. 5 shows a schematic view of a cooling system according to a second embodiment of the application,

FIG. 6 shows a schematic view of a cooling system according to a third embodiment of the application, and

FIG. 7 shows a schematic view of a cooling system according to a fourth embodiment of the application.

DETAILED DESCRIPTION OF THE APPLICATION

FIG. 1 shows a schematic view of a cooling system 2 according to a first embodiment of the application for cooling at least one heat generating radio unit 4, 6, 8 in an active antenna system unit 10, the cooling system 2 comprising at least one fan 12 and an air duct 14, where each heat generating radio unit 4, 6, 8 to be cooled by the cooling system 2 is arranged connected to a heat sink unit 16, 18, 20 comprising cooling fins 22, 24, 26, 28, 30, 32, the heat sink unit 16, 18, 20 being arranged to transfer heat between the radio unit 4, 6, 8 and the ambient air 34, where the at least one fan 12 is arranged to generate a primary air flow 33 of ambient air 34 in the air duct 14 between at least one air duct inlet 36 and at least one air duct outlet 38, where the air duct 14 is arranged to extend in the longitudinal direction A of the active antenna system unit 10 along each of the said heat sink units 16, 18, 20 and to border on each of the said heat sink units 16, 18, 20 where the primary air flow 33 generated in the air duct 14 is arranged to flow substantially in the longitudinal direction A of the active antenna system unit 10 and is further arranged to generate a secondary air flow 35 of ambient air 34 over a number of cooling fins 22, 24, 26, 28, 30, 32 of each of the said heat sink units 16, 18, 20, where the cooling fins 22, 24, 26, 28, 30, 32 are arranged oriented at an angle α with respect to the longitudinal direction A of the active antenna system unit 10.

By arranging the cooling fins 22, 24, 26, 28, 30, 32 to be cooled by the secondary air flow 35 to be oriented at an angle α with respect to the longitudinal direction A of the active antenna system unit 10, the longitudinal extension C of the cooling fins 22, 24, 26, 28, 30, 32 to be cooled by the ambient air flow can be reduced when comparing with traditional designs, whereby the temperature of the ambient air flow at the downstream end of the respective cooling fin 22, 24, 26, 28, 30, 32 can be reduced, thus increasing the cooling power at this position of the respective heat sink unit 16, 18, 20 which is especially advantageous when using radio units 4, 6, 8 with heat sinks units 16, 18, 20 having large dimensions in the longitudinal direction A of the active antenna system unit 10. A further advantage is that the air duct 14 and the at least one fan 12 do not affect the natural cooling when the at least one fan 12 is shut off in situations where forced cooling is not needed, e.g. when the ambient temperature is so low that natural cooling is enough. According to this embodiment, the at least one fan 12 is arranged to generate a primary air flow 33 of ambient air 34 in the air duct 14 between at least one air duct inlet 36 and at least one air duct outlet 38 by introducing ambient air 34 into the air duct 14 from at least one air duct inlet 36 and where the air duct outlet 38 is arranged to direct a flow of ambient air 34 over a number of cooling fins 22, 24, 26, 28, 30, 32 of each of the said heat sink units 16, 18, 20, where the cooling fins 22, 24, 26, 28, 30, 32 are arranged oriented at an angle with respect to the longitudinal direction A of the active antenna system unit 10.

The active antenna system unit 10 comprises at least one heat generating radio unit 4, 6, 8 and at least one antenna 40 both arranged along the longitudinal direction A of the active antenna system unit 10, and further comprises a cooling system for cooling at least one heat generating radio unit 4, 6, 8, where the respective radio unit 4, 6, 8 is installed or mounted directly on the antenna (i.e. semi-integrated) or integrated with the antenna (i.e. integrated).

The at least one fan 12 is preferably a centrifugal fan arranged at one end of the air duct 14 arranged at one longitudinal side of the active antenna system unit 10.

The at least one fan 12 and the air duct 14 can be arranged as two individual parts that are assembled together on site, or be arranged as an integrated unit.

FIG. 2 shows another schematic view of the cooling system 2 according to FIG. 1, where the direction of flow of ambient air 34 is schematically shown in the figure. As shown in the figure, the ambient air 34 is introduced into the air duct 14 at at least one air duct inlet 36, flows 33 through the air duct 14 along the longitudinal direction A of the active antenna system unit 10, and leaves the air duct 14 at least one air duct outlet 38 directing a flow 35 of ambient air 34 over a number of cooling fins 22, 24, 26, 28, 30, 32 of each of the said heat sink units 16, 18, 20, where the cooling fins 22, 24, 26, 28, 30, 32 are arranged oriented at an angle α with respect to the longitudinal direction A of the active antenna system unit 10.

FIG. 3 shows a schematic cross-section of an air duct according to the first embodiment of the application. The cross-section is taken along the longitudinal direction A of the active antenna system unit 10. The at least one fan 12, the at least one air duct inlet 36 and the air duct outlet 38 are schematically shown in the figure. As is shown in the figure, the air duct outlet 38 can be arranged to extend along one end of the majority of the cooling fins 22, 24, 26, 28, 30, 32 of each of the said heat sink units 16, 18, 20, and the gap size B of the air duct outlet 38 may further be arranged with varying dimensions, e.g. narrowing gap shape, along the extension of the air duct 14 in the longitudinal direction A of the active antenna system unit 10 in order to enable uniform outlet flow of air at the outlet 38 in order to enable substantially uniform cooling along all said cooling fins 22, 24, 26, 28, 30, 32.

FIG. 4 shows another schematic cross-section of an air duct according to one embodiment of the application. The cross-section is taken transversally to the extension of the air duct 14, i.e. at a right angle to the cross-section shown in FIG. 3. The air duct 14 and the air duct outlet 38 are shown in the figure. The direction of the secondary air flow 35 outside the outlet 38 is also indicated in the figure. In order to direct the secondary air flow outside the air duct outlet 38 towards the surface of the heat sink unit 16, 18, 20, a cover 42 can be arranged at the air duct 14 to direct the secondary air flow 35 over the cooling fins 22, 24, 26, 28, 30, 32. In order to enable air flow for natural cooling when the at least one fan is not in operation, the cover 42 preferably covers the heat sink units 16, 18, 20 only partly.

The design with the air duct 14 arranged along a longitudinal side of the active antenna system unit 10 does not affect the natural cooling when the at least one fan is shut off when forced cooling is not needed.

In the figure, the relative position of the cooling fins 22, 24, 26, 28, 30, 32, the at least one heat generating radio unit 4, 6, 8, and the at least one antenna 40 are schematically indicated.

As is shown in the figure, it is possible to arrange a cooling fin 22, 24, 26, 28, 30, 32 with varying dimensions, e.g. differing height, along the longitudinal extension C of the cooling fin 22, 24, 26, 28, 30, 32 in order to enable more uniform cooling of the at least one heat generating radio unit 4, 6, 8 along the length of said cooling fins 22, 24, 26, 28, 30, 32.

FIG. 5 shows a schematic view of a cooling system according to a second embodiment of the application. The embodiment shown in FIG. 5 differs from the embodiment shown in FIG. 2 in that the at least one fan 12 is arranged outside the air duct 14 at one end of the air duct 14. The direction of flow 33, 35 of ambient air 34 is schematically shown in the figure.

According to this embodiment, the at least one fan 12 is arranged to generate a primary air flow 33 of ambient air 34 in the air duct 14 between at least one air duct inlet 36 and at least one air duct outlet 38 by introducing ambient air 34 into the air duct 14 from at least one air duct inlet 36 and where the air duct outlet 38 is arranged to direct a flow of ambient air 34 over a number of cooling fins 22, 24, 26, 28, 30, 32 of each of the said heat sink units 16, 18, 20, where the cooling fins 22, 24, 26, 28, 30, 32 are arranged oriented at an angle α with respect to the longitudinal direction A of the active antenna system unit 10.

FIG. 6 shows a schematic view of a cooling system according to a third embodiment of the application. The embodiment shown in FIG. 6 differs from the embodiment shown in FIG. 2 in that the air duct is arranged with its air duct inlet 36 along a longitudinal side of the active antenna system unit 10. The direction of flow 33, 35 of ambient air 34 is schematically shown in the figure.

According to this embodiment, the at least one fan 12 is arranged to generate a primary air flow 33 of ambient air 34 in the air duct 14 between at least one air duct inlet 36 and at least one air duct outlet 38 by introducing ambient air 34 into the air duct 14 from at least one air duct inlet 36 arranged along a longitudinal side of the active antenna system unit 10, and where the air duct inlet 36 is arranged to suck a secondary air flow 35 of ambient air 34 over a number of cooling fins 22, 24, 26, 28, 30, 32 of each of the said heat sink units 16, 18, 20, where the cooling fins 22, 24, 26, 28, 30, 32 are arranged oriented at an angle with respect to the longitudinal direction A of the active antenna system unit 10.

According to this embodiment, the air duct inlet 36 can be arranged to extend along one end of the majority of the cooling fins 22, 24, 26, 28, 30, 32 of each of the said heat sink units 16, 18, 20, and the gap size B of the air duct inlet 36 may further be arranged with varying dimensions, e.g. narrowing gap shape, along the extension of the air duct 14 in the longitudinal direction A of the active antenna system unit 10 in order to enable uniform inlet flow of air at the inlet 36 in order to enable substantially uniform cooling along all said cooling fins 22, 24, 26, 28, 30, 32.

FIG. 7 shows a schematic view of a cooling system according to a fourth embodiment of the application. The embodiment shown in FIG. 7 differs from the embodiment shown in FIG. 6 in that the at least one fan 12 is arranged outside the air duct 14 at one end of the air duct 14, and in that only one radio unit 4 with heat sink unit 16 is arranged in the active antenna system unit 10. The direction of flow 33, 35 of ambient air 34 is schematically shown in the figure.

According to this embodiment, the at least one fan 12 is arranged to generate a primary air flow 33 of ambient air 34 in the air duct 14 between at least one air duct inlet 36 and at least one air duct outlet 38 by introducing ambient air 34 into the air duct 14 from at least one air duct inlet 36 arranged along a longitudinal side of the active antenna system unit 10, and where the air duct inlet 36 is arranged to suck a secondary air flow 35 of ambient air 34 over a number of cooling fins 22, 24 of each of the said heat sink units 16 where the cooling fins 22, 24 are arranged oriented at an angle with respect to the longitudinal direction A of the active antenna system unit 10.

The application also relates to a method for cooling at least one heat generating radio unit 4, 6, 8 in an active antenna system unit 10 using a cooling system 2, the cooling system 2 comprising at least one fan 12 and an air duct 14, comprising the steps of: connecting each heat generating radio unit 4, 6, 8 to be cooled by the cooling system 2 to a heat sink unit 16, 18, 20 comprising cooling fins 22, 24, 26, 28, 30, 32, arranging the heat sink unit 16, 18, 20 to transfer heat between the radio unit 4, 6, 8 and the ambient air 34, arranging the at least one fan 12 to generate a primary air flow 33 of ambient air 34 in the air duct 14 between at least one air duct inlet 36 and at least one air duct outlet 38, arranging the air duct 14 to extend in the longitudinal direction A of the active antenna system unit 10 along each of the said heat sink units 4, 6, 8 and to border on each of the said heat sink units 4, 6, 8, arranging the primary air flow 33 generated in the air duct 12 to flow substantially in the longitudinal direction A of the active antenna system unit 10 and further arranging the primary air flow 33 to generate a secondary air flow 35 of ambient air 34 over a number of cooling fins 22, 24, 26, 28, 30, 32 of each of the said heat sink units 4, 6, 8, and arranging the cooling fins 22, 24, 26, 28, 30, 32 to be cooled by the secondary air flow 35 to be oriented at an angle α with respect to the longitudinal direction A of the active antenna system unit 10.

The method for cooling a heat generating unit 4 can further comprise the step of arranging the at least one air duct outlet 38 to direct a flow of ambient air 34 over a number of cooling fins 22, 24, 26, 28, 30, 32 of each of the said heat sink units 16, 18, 20, or can further comprise the step of arranging the at least one air duct inlet 36 to suck a secondary air flow 35 of ambient air 34 over a number of cooling fins 22, 24, 26, 28, 30, 32 of each of the said heat sink units 16, 18, 20.

The application has been described using straight cooling fins, but it is also possible to arrange the cooling fins with other shapes along their longitudinal extension such as e.g. to arrange a cooling fin wave formed or with curved shape along the longitudinal extension of the cooling fin. The angle α between a cooling fin and the longitudinal direction A of the active antenna system unit 10 can also be arranged to vary along the extension C of the cooling fin.

The present application is not limited to the embodiments described above, but also relates to and incorporates all embodiments within the scope of the appended independent claim. Thus, it is possible to combine features from the embodiments described above as long as the combinations are possible. 

1. Cooling system for cooling at least one heat generating radio unit in an active antenna system unit, the cooling system comprising at least one fan and a single air duct, wherein each heat generating radio unit to be cooled by the cooling system is arranged connected to a heat sink unit comprising cooling fins, the heat sink unit being arranged to transfer heat between the radio unit and the ambient air, wherein the at least one fan is arranged to generate a primary air flow of ambient air in the single air duct between at least one air duct inlet and at least one air duct outlet, wherein the at least one air duct inlet, the single air duct and the at least one air duct outlet are arranged to extend in a same longitudinal direction (A) of the active antenna system unit along a same side which borders each of the heat sink units, wherein the primary air flow generated in the single air duct is arranged to flow substantially along the same longitudinal direction (A) of the active antenna system unit and is further arranged to generate along the same side which borders each of the heat sink units, a secondary air flow of ambient air over a number of cooling fins of each of the said heat sink units, wherein the cooling fins are obliquely arranged and oriented at an angle with respect to the longitudinal direction (A) of the active antenna system unit.
 2. Cooling system according to claim 1, wherein the at least one air duct outlet is arranged to direct a flow of ambient air over a number of cooling fins of each of the said heat sink units.
 3. Cooling system according to claim 2, wherein the at least one air duct outlet is arranged along a longitudinal side of the active antenna system unit.
 4. Cooling system according to claim 2, wherein the gap size (B) of the air duct outlet is arranged with varying dimensions along the longitudinal direction (A) of the active antenna system unit.
 5. Cooling system according to claim 4, wherein the air duct outlet is arranged with narrowing gap size (B) along the longitudinal direction (A) of the active antenna system unit.
 6. Cooling system according to claim 2, wherein a cover is arranged at the air duct to direct the secondary air flow over the cooling fins.
 7. Cooling system according to claim 2, wherein the angle (α) between a cooling fin and the longitudinal direction (A) of the active antenna system unit is arranged to vary along the extension (C) of the cooling fin.
 8. Cooling system according to claim 2, wherein a cooling fin is arranged with varying dimensions along the longitudinal extension (C) of the cooling fin.
 9. Cooling system according to claim 2, wherein a cooling fin is arranged in a wave formed shape or arranged in a curved shape along the longitudinal extension (C) of the cooling fin.
 10. Cooling system according to claim 2, wherein the at least one fan is a centrifugal fan.
 11. Cooling system according to claim 1, wherein the at least one air duct inlet is arranged to suck a secondary air flow of ambient air over a number of cooling fins of each of the said heat sink units.
 12. Cooling system according to claim 11, wherein the at least one air duct inlet is arranged along a longitudinal side of the active antenna system unit.
 13. Cooling system according to claim 11, wherein the gap size (B) of the air duct inlet is arranged with varying dimensions along the longitudinal direction (A) of the active antenna system unit.
 14. Cooling system according to claim 11, wherein the air duct inlet is arranged with narrowing gap size (B) along the longitudinal direction (A) of the active antenna system unit.
 15. Cooling system according to claim 11, wherein a cover is arranged at the air duct to direct the secondary air flow over the cooling fins.
 16. Cooling system according to claim 11, wherein the angle (α) between a cooling fin and the longitudinal direction (A) of the active antenna system unit is arranged to vary along the extension (C) of the cooling fin.
 17. Cooling system according to claim 11, wherein a cooling fin is arranged with varying dimensions along the longitudinal extension (C) of the cooling fin.
 18. Cooling system according to claim 11, wherein a cooling fin is arranged wave formed or with curved shape along the longitudinal extension (C) of the cooling fin.
 19. Cooling system according to claim 11, wherein the at least one fan is a centrifugal fan.
 20. Method for cooling at least one heat generating radio unit in an active antenna system unit using a cooling system, the cooling system comprising at least one fan and a single air duct, characterized by comprising the steps of: connecting each heat generating radio unit to be cooled by the cooling system to a heat sink unit comprising cooling fins; arranging the heat sink unit to transfer heat between the radio unit and the ambient air; arranging the at least one fan to generate a primary air flow of ambient air in the single air duct between at least one air duct inlet and at least one air duct outlet; arranging the at least one air duct inlet, the single air duct and the at least one air duct outlet to extend in a same longitudinal direction (A) of the active antenna system unit along a same side which borders each of the heat sink units; arranging the primary air flow generated in the single air duct to flow substantially along the same longitudinal direction (A) of the active antenna system unit; arranging the primary air flow to generate along the same side which borders each of the heat sink units, a secondary air flow of ambient air over a number of cooling fins of each of the said heat sink units; and arranging the cooling fins to be cooled by the secondary air flow, wherein the secondary fins are obliquely oriented at an angle (α) with respect to the longitudinal direction (A) of the active antenna system unit.
 21. Method for cooling a heat generating unit (4) according to claim 20, further comprising the step of arranging the at least one air duct outlet to direct a flow of ambient air over a number of cooling fins of each of the said heat sink units.
 22. Method for cooling a heat generating unit (4) according to claim 17, further comprising the step of arranging the at least one air duct inlet to suck a secondary air flow of ambient air over a number of cooling fins of each of the said heat sink units. 